func expand<%= prefix -%><%= titlelize_property(property) -%>(v interface{}, d TerraformResourceData, config *Config) (interface{}, error) {
  if v == nil || v.(string) == "" {
    return "", nil
  } else if strings.HasPrefix(v.(string), "https://") {
    return v, nil
  }
  url, err := replaceVars(d, config, "{{ServiceDirectoryBasePath}}" + v.(string))
  if err != nil {
    return "", err
  }
  return url, nil
}
